[Milsurplus] ARC 65 vs. ARC 58

[Ray Fantini]

This is all speculation on my part being that the ARC-21 and up converted ARC-65 are radios I have not had the opportunity to work with yet but do have some experience with other radios of that time and can speculate that because the PA and receiver for the ARC- 21/65 were designed originally for AM service they may lend themselves better to a mode of operation like RTTY then an SSB designed transceiver like the ARC-58. The ARC-21 PA deck and HV power supplies had to provide full carrier output in AM service and the power supply had to not only power the PA it also had to power a very hungry modulator when in AM service. In comparison a SSB transceiver almost never operates for prolonged periods at full output and often has to operate at a lower power level when in CW or RTTY modes. Receivers designed for AM/RTTY service often have way simpler AGC systems then SSB radios and the slower acting AGC of those receivers often works better than the fast acting AGC of a SSB radio. The ARC-58/TRC-75 is great radio for SSB operation and I know it close relative the URC-32 while primarily being a SSB radio also supported RTTY, but I do know from firsthand experience that sometimes more modern radios preform poorer in certain modes then the ones they replace, look at something like operating CW The old ARC-38 and the 618S series of AM transceivers way outperform newer radios like the 618T when using CW, the old ARC-38 has a variable BFO, it has a narrow bandwidth CW filter that the operator can switch in and out, separate RF and AF gain controls and a CW SEND/ STBY mode all make it easy for the operator and perform well on CW. By comparison the 618T that replaces the 38 was a dog on CW, but the 618T in voice mode operations far surpasses every aspect of the older ARC-38 and modified for SSB ARC-38A set in every way. With SSB being the future and CW the past can see exactly why and how things were decided and done. Maybe there was some small advantage in the RTTY mode in the ARC-21/65 favor but the future required dependable SSB voice and data modes and the ARC-58/TRC-75 was the future. 
RF